A wide variety of conditions, including infection by bacteria, viruses or fungi, infiltration by cancer cells, allergic or autoimmune disorders and physically- or chemically-induced trauma, cause inflammatory responses in humans. In all of these diseases and conditions in man and in most mammals, activation of the complement system (a set of proteins, regulatory factors and proteolytic enzymes) via either the classical or the alternative pathway, results in the generation of biologically-active peptides which serve to amplify and exacerbate the resulting inflammation.
The most active peptide, anaphylatoxin C5a, a 74-amino acid polypeptide which is released during the activation of serum complement proteins, is generated by cleavage of the alpha-chain of native C5 at a specific site by convertases (proteolytic enzymes) of the blood complement system, as well as by enzymes of the coagulation system. C5a exists in vivo in two biologically-active forms. Once it is liberated from C5, the carboxyl-terminal arginine of C5a is rapidly removed by carboxypeptidase-N, leaving the des-Arg derivative. Although C5a des-Arg is less active than C5a, both are potent inflammatory mediators at concentrations likely to be generated in vivo (Fernandez, H. N.; Henson, P. M.; Otani, A. and Hugli, T. E., J. Immunol. 1978, 120, 109). Together, these peptides, along with C3a, C4a, and their des-Arg degradation products, collectively described herein as anaphylatoxin, are capable of triggering diverse inflammatory reactions (Hugli, T. E. and Muller-Eberhard, H. J., Adv. Immunol. 1978, 26, 1-53; Hugli, T. E., Crit. Rev. Immunol 1981, 1, 321-366; Frank, M. M. and Fries, L. F., Immunol. Today 1991, 12, 322-326; Goldstein, I. M. in Inflammation: Basic Principles and Clinical Correlates 1992, (Gallin, J. I.; Goldstein, I. M. and Snyderman, R., eds), pp 63-80, Raven Press; and Hugli, T. E., Stinger Semin. Immunopathol. 1984, 7, 193-219). C5a is believed to play a major role as a potent inflammatory mediator by its additional activities in recruiting and stimulating inflammatory leukocyctes.
Once liberated from its parent molecule, C5a interacts with specific membrane receptors present on white blood cells including polymorphonuclear leukeocytes (PMNL), monocytes, basophils, and eosinophils, as well as with tissue resident cells such a macrophages and mast cells. Among the various cell types, the neutrophil response to C5a is the best defined. Chenoweth and Hugli (Chenoweth, D. E. and Hugli, T. E., Proc. Nat. Acad. Sci. U.S.A. 1978, 75, 3943-3947) have shown that binding of human C5a to intact polymorphonuclear leukocytes is saturable and specific, and effected the induction of a cellular response. Cell surface receptors specific for C5a have been demonstrated on the neutrophil (Huey, R. and Hugli, T. E., J. Immunol. 1985, 135, 2063-2068; and Rollins, T. E. and Springer, M. S., J. Bio. Chem. 1985, 260, 7157-7160), and the ligand-receptor interaction has been shown to promote human polymorphonuclear leukocyte (PMNL) migration in a directed fashion (chemotaxis) (Frank, M., Rev. Infectious Diseases 1979, 1(3), 483-501), adherence, oxidative burst, and granular enzyme release from these cells (Hugli, T. E., Springer Semin. Immunopathol. 1984, 7, 193-219). The interaction of C5a with PMN and other target cells and tissues results in increased histamine release, vascular permeability, smooth muscle contraction, and an influx into tissues of inflammatory cells, including neutrophils, eosinophils, and basophils (Hugli, T. E., Springer Semin. Immunopathol. 1984, 7, 193-219).
C5a may also be important in mediating inflammatory effects of phagocytic mononuclear cells that accumulate at sites of chronic inflammation (Allison, A. C.; Ferluga, J.; Prydz, H. and SCherlemmer, H. U., Agents and Actions 1978, 8, 27). C5a and C5a des-Arg can induce cherootaxis in monocytes (Ward, P. A., J. Exp. Med. 1968, 128, 1201; and Snyderman, R.; Shin, H. S. and Dannenberg, A. C., J. ImmunoL 1972, 109, 896) and cause them to release lysosomal enzymes (McCarthy, K. and Henson, P. S., J. Immunol. 1979, 123, 2511) in a manner analogous to the neutrophil responses elicited by these agents. In addition, recent studies suggest that C5a may have an immunoregulatory role by enhancing antibody particularly at sites of inflammation (Morgan, E. L.; Weigle, W. O. and Hugli, T. E., J. Exp. Med. 1982, 155, 1412; Weigle, W. O.; Morgan, E. L.; Goodman, M. G.; Chenoweth, D. E. and Hugli, T. E., Federation Proc. 1982, 41, 3099; and Morgan, E. L.; Weigle, W. O. and Hugli, T. E., Federation Proc. 1984, 43, 2543).
C5a and C5a des-Arg additionally play important roles in host defenses against bacterial infections and possibly in the mediation of some pathologic lesions such as the leukocyte infiltration seen in the lungs during acute respiratory distress syndrome. This mechanism seems to play a role in different pathological situations like pulmonary distress during hemodialysis, leukophoresis, cardiopulmonary bypass, and in acute myocardial infarction. Complement activation has been postulated to play an important pathological role in rheumatoid arthritis, serum sickness, systemic lupus erythematosus, ulcerative colitis, and forms of hepatic cirrhosis, chronic hepatitis, and glomerulonephitis, in certain shock states, during hemodialysis, and cardiopulmonary bypass, acute pancreatitis, myocardial infarction (which may be worsened by C5a-induced leuko-embolization following the interaction of complement with atheromatous plaques), asthma, bronchoconstriction, some auto-allergic diseases, transplant rejection, and post-viral encephalopathies.
Thus, the search for specific C5a receptor antagonists to bind to and block the anaphylatoxin receptor and thus prevent or reduce anaphylatoxin-mediated inflammation, and C5a receptor agonists to assist the body in building its defense mechanisms against invasion by infectious agents and malignancy, as well as possibly influencing the immunoregulatory effects of anaphylatoxin, has been an active and ongoing process in recent years because of its therapeutic implications.
The search has centered on the C5a receptor binding affinity of compounds, based on the results of numerous studies which support the conclusion of a strong correlation between in vitro binding of a compound at the C5a receptor and its ability to modulate the in vitro and in vivo response of those cells to which C5a also binds, that is, to modulate C5a activity (Gerard, C., et al., J. ImmunoL 1981, 127, 1978-1982; Johnson, R. J. and Chenoweth, D. E., J. Biol Chem., 1985, 260, 10339-10345; Swerlick, R. A., et al., J. Immunol., 1988, 140, 237-238; and Mollison, K. W., et al., Proc. Natl. Acad. Sci. USA, 1989, 86, 292-296). "It is precisely the receptor-ligand interactions that classify anaphylatoxins as local hormones and cellular reactions to ligand binding that escalates the functional impact of these complement factors to systemic proportions" (Hugli, T. E., Springer Semin. Immunopathol. 1984, 7, 195).
Although most studies have addressed the in vitro properties of human C5a and C5a receptor binding analogues, in vivo studies with human volunteers showed that human C5a des Arg-74 can elicit inflammatory responses in human skin, but C5a des Arg-74 was less potent than native C5a (Swerlick et al, op.cit.). The difference between native C5a and C5a des Arg-74 activity in vivo is consistent with the lower in Vitro C5a receptor binding afffinity that was reported for C5a des Arg-74 (Gerard et al., op.cit.).
Once the identity of a compound which binds to the C5a receptor has been made, the methods are well known to determine whether the compound is functioning as a C5a agonist or antagonist (Hugli, T., "The Structural Basis for Anaphylatoxin and Chemotactic Functions of C3a, C4a and C5a", Chapter 4, pages 321-366 in Critical Reviews in Immunology, I, CRC Press, Boca Raton, Fla. (1981)).
Thus, the novel antagonists and agonists of the present invention represent useful agents in this field. The possible involvement of anaphylatoxin in a wide range of diseases, as indicated by the examples above, suggests that anaphylatoxin receptor ligands could have clinical applications for the treatment and prevention of serious pathological conditions.
Kawai et al., U.S. Pat. No. 5,223,485, issued Jun. 29, 1993, discloses and claims C5a receptor antagonists having 7-12 amino acid residues, which neither anticipate nor suggest the compounds of the instant invention. The present invention's unique C-terminal dipeptide fragment of "homohomoarylalanyl" (that has a three atom chain between the aryl moiety and the asymmetric carbon atom) at the M position which is coupled to the .alpha.-amino group of the C-terminal arginine residue, among other differences, clearly distinguishes the novel compounds of the present invention.